Cross-encoding of information in independent channels

ABSTRACT

Independent first and second information signals (content 1  and content 2 ) are transmitted over separate independent physical channels to a receiving location. Security is provided by encoding ( 12   a ) at least the first information by means of the second information to produce encoded signals ( 1′, . . .  N′). The encoded signals and the second signals are received from the first and second channels at the second location ( 230 ). The encoded first signals are decoded at the receiving location by processing with the second signals. In some embodiments, the second information signals are encoded by processing with the first information signals. In a more general case, plural channels of information are “cross-encoded” by the information in plural other channels, and the plurality may be large.

CROSS-ENCODING OF INFORMATION IN INDEPENDENT CHANNELS

This application claim the benefit, under 35 U.S.C. § 365 ofInternational Application PCT/US 2004/007114 filed Mar. 9, 2004, whichwas published in accordance with PCT Article 21(2) on Oct. 20, 2005 inEnglish.

FIELD OF THE INVENTION

This invention relates to the encoding of information, and moreespecially to encoding of first information traversing a first channelto a location by means of second information traversing a second channelto the location.

BACKGROUND OF THE INVENTION

Current television and or radio services often provide pay-per-use orconditional access to program content. Customers who do not pay for theprivilege of receiving the content are prevented from receiving thesignals by encoding, and often by encrypting, the signals which containthe content. The term “encoding” is used herein for encoding,scrambling, and encrypting, and “decoding” for decoding, descrambling,and decryption. Paying customers receive a decoding key so that they maydecode the encoded content for use.

Unfortunately, some persons may receive the encoded signal and extractthe key, either on- or off-line, and may thereby avoid paying the feefor use of the content. FIG. 1 is a simplified block diagram of a cabletelevision system 10 including one subscriber. In the system of FIG. 1,video or music content 1, which is to be made available as pay-per-view,is applied to an encoder 12 a. Encoder 12 a encodes the content with theaid of a key produced by a key generator 14 a, which is applied to aninput port 12 ai, to produce encoded first content. The encoded firstcontent produced by encoder 12 a is applied to a frequency upconverter16 a, which converts the frequency to a unique frequency range orchannel, centered on a frequency f1. Second content 2, which is to bemade available to all subscribers, is applied directly to a secondfrequency upconverter 16 b, which converts the unencoded content to asecond unique frequency range. System 10 of FIG. 1 includes otherfrequency upconverters and may include other encoders, such as encoder12N, which encodes content N by means of a key, which may be the samekey as that used for encoder 12 a, or which may be a different key froma generator 14N, applied to its encoding input port 12Ni. The encodedoutput of encoder 14N is applied to an upconverter 16N for conversion toa frequency range fN, different from the other frequency ranges. Theencoded and unencoded signals on frequencies f1, f2, . . . , fN areapplied to a frequency-sensitive combiner 18, which combines the signalsonto a single path, which is the system television transmission path orline 20 (which may be a coaxial cable or an optical fiber).

The many carriers at the various frequencies f1, f2, . . . , fN flowalong the cable 20 toward the subscribers. It should be understood thateach separate carrier frequency on the cable system 10 constitutes asingle channel which carries only one content. At any given subscriber'slocation, a portion of the signal including carriers f1, f2, . . . , fNis removed from the transmission path 20, as by a directional coupler22, and carried to the subscriber's location, designated 24 in FIG. 1.At the subscriber, the signal is made available either directly to atelevision receiver 26, or if the system carrier frequencies aredifferent from conventional television carrier frequencies, or ifdecoding of content are desired, the signal is made available to thetelevision receiver 26 by way of a receiver/decoder 30. Receiver/decoder30 receives only one channel, so receives from the cable only onechannel.

When the subscriber at location 24 wishes to view unrestricted content,the television receiver 26 or the receiver portion of receiver/decoder30 is set to select the appropriate one of the frequency ranges flowingin transmission path 20 (the desired channel), and the content may beviewed or listened to without more.

If the subscriber wishes to use conditionally restricted content, thetelevision receiver (or monitor) 26 or the receiver portion ofreceiver/decoder 30 is set to select the appropriate one of thefrequency ranges flowing in transmission path 20. However, this isinsufficient to allow the content to be used. In order to use theconditionally restricted content, the subscriber must obtain a suitabledecoding key for use in operating the decoding algorithm at hisreceiver/decoder. Many methods of obtaining the key are known, such aspurchase of a card in a bricks-and-mortar store. One known way to obtaina key is for the subscriber to use a telephone to call a service centeraffiliated with the cable company, identify himself and make theappropriate payment, and receive the key electronically over thetransmission path 20 of FIG. 1.

Some persons may attempt to obtain the use of the conditionallyrestricted content by storing the encoded content in a memory associatedwith a computer, and using the processing power of the computer toattempt to determine the encoding key or algorithm. In FIG. 1, a sampleof the signal received from the receiver/decoder 30 at location 24 ismade available to a computer 34. Computer 34 may be used to store thekey transmitted over path 20, the encoded signal received by thereceiver portion of receiver/decoder 30, or both. With the key and orsignal stored, it or they can be manipulated by computer algorithms toattempt to extract the encoding algorithm, key, or both. With thatinformation available, the encrypted information content becomesavailable to the subscriber at location 24, notwithstanding that he hasnot paid for the content.

Improved methods are desired for protection of information againstunauthorized use.

SUMMARY OF THE INVENTION

A method according to an aspect of the invention is for securelytransmitting first information from a first location to a secondlocation by way of a first channel. The method comprises the steps of,at the first and second location, acquiring second and additionalinformation which is independent of the first information, and timealigning the second and additional information at both the first andsecond locations. At the first location, the first information isrelated with the second and additional information by means of a firstfunction to thereby generate a transmitter signal for transmission, andthe resulting signal is transmitted from the first location to thesecond location by way of a first signal channel. At the secondlocation, the transmitter signal is related to the second and additionalinformation with a second function which is the reverse of the firstfunction, to thereby recover the first information. In one particularmode of the method, the first and second functions are XOR functions.The step of acquiring the second and additional information at thesecond location may includes the steps of receiving the second andadditional information by way of individual, independent signalchannels. In a particularly advantageous version of this method, atleast some of the second and additional information is transmitted fromthe first location to the second location. The step of transmitting atleast some of the second and additional information from the firstlocation to the second location may be performed by way of at least onesignal channel independent of the first signal channel. The step oftransmitting at least some of the second and additional information fromthe first location to the second location may be performed bytransmitting each of the second and additional information by way of asingle signal channel independent of the first signal channel for eachindividual one of the second and additional information. In aparticularly advantageous version of the method, the step of at thesecond location, relating the transmitter signal to the second andadditional information with a second function, is performed in concertwith a receiver able to simultaneously receive multiple channelsincluding the first signal channel, and the signal channels for eachindividual one of the second and additional information.

A method according to an aspect of the invention is for securelytransmitting first and second information from a first location to asecond location. The method comprises the step of processing the firstinformation by means of at least the second information to therebygenerate processed first information. The second information isprocessed by means of at least the first information to thereby generateprocessed second information. The processed first and second informationare transmitted separately by way of independent first and secondphysical channels, respectively, to the second location. At the secondlocation the processed first information is reverse processed by use ofat least the processed second information. Reverse processing of theprocessed second information may be done by the use of at least theprocessed first information.

In a particular mode of the method, the step at the second location ofreverse processing the processed first information by use of at leastthe processed second information includes the step of independentlyreceiving the processed first information from the first independentchannel and independently receiving the processed second informationfrom the second independent channel. In a preferred mode of this method,this latter step is performed in or by an integrated circuit.

According to another aspect of the invention, a receiver is provided forsimultaneously recovering at least first information received inprocessed form by way of a first independent physical channel and secondinformation by way of a second independent physical channel. The firstinformation transmitted over the first physical channel is processedbefore transmission in conjunction with second information to generateprocessed or encoded information. The second information is transmittedto the receiver over a second independent channel. The receivercomprises means for receiving the processed first information from thefirst physical channel, and also comprises means for receiving thesecond information from the second independent channel. A processingmeans processes the first processed information in conjunction with thesecond information to extract the first information from the firstprocessed information. In that case in which the information transmittedover the second channel is encoded to form second processed information,the processing means also extracts the original second information, andfor this purpose the receiver comprises further processing means forprocessing the first processed information with the second informationto extract information relating to the form of the second informationbefore the processing with the first information.

In a preferred embodiment of this receiver, all or most of the describedfunctions are contained or lie within a single integrated circuit.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a simplified block diagram of a “cable television” systemsimilar to those of the prior art, with one subscriber connection of thecable signal to a computer;

FIG. 2 is a simplified block diagram of a system cable television systemsimilar to that of FIG. 1, and including connections related to theinvention;

FIG. 3 is a simplified block diagram representing an alternativeconnection arrangement for a portion of FIG. 2;

FIG. 4 illustrates a logic flow in an exemplary digital satellite andtransmission system in accordance with the present principles; and

FIG. 5 is a simplified block diagram of an overall communications systemaccording to an aspect of the present principles.

DESCRIPTION OF THE INVENTION

The invention makes use of multiple physical channels, corresponding, inthe case of a cable television system, to separate (frequency-separated)channels. According to an aspect of the invention, the encoding of theconditionally restricted content flowing in one channel is performed bythe use of information flowing in another channel of the system. In FIG.2, a cable television system 210 is similar to the system of FIG. 1. Asalient difference between the arrangement of FIG. 2 by comparison withthat of FIG. 1 is that the key generators 14 a, . . . , 14N of FIG. 1are not used in the arrangement of FIG. 2. Instead, each encoder 14 a, .. . , 14N receives, as its encoding stream, the information content ofanother channel. More particularly, in the arrangement of FIG. 1, firstencoder 12 a receives at its encoding signal input port 12 ai the clearinformation content N, and N^(th) encoder 12N receives at its encodingsignal input port 12Ni clear information content 1.

As in the arrangement of FIG. 1, the encoded information content 1′ fromencoder 12 a, is upconverted and applied at frequency f1 to transmissionpath 20 by combiner 18. Independently, the clear or unencoded content 2is upconverted, and made available at frequency f2 on transmission path20, and the encoded content N′ of encoder 12N is upconverted byupconverter N, and made available at frequency fN on the transmissionpath.

At subscriber location 24 of FIG. 2, the combined signal from thetransmission path 20 is made available by means of directional coupler22. Unlike the arrangement of FIG. 1, the receiving arrangement 230 ofFIG. 2 includes a set 240 including a plurality 240 a, 240 b , . . . ,240M of individual receivers, each capable of receiving content from oneindependent physical channel. The number of individual receivers inreceiving arrangement 230 depends upon the number of channels which areused to perform encoding. Thus, in the arrangement as illustrated inFIG. 2, encoder 12 a encodes content channel 1 with information fromcontent channel 3, and encoder 12N encodes content channel N withinformation from content channel 1. Thus, only one additional channel ofinformation is necessary to decode either content 1 or content N, soonly two individual receivers 240 a, 240 b (or 240 a, 240M, or any otherset of two receivers) are needed to produce the two channels of content.If the information of content channel 1 were to be encoded by means ofinformation from five or ten other channels, then the receivingarrangement 230 of FIG. 2 would require six or eleven receivers,respectively (one for the content channel, five or ten for the encodinginformation).

The encoded content from the desired number of receivers of set 240 ofindividual receivers of receiving arrangement 230 is applied to adecoder illustrated as a box designated 242. Decoder block 242 decodesat least one of the contents, such as content 1. It also has available,in the particular encoding arrangement illustrated in FIG. 2, theinformation required to decode two individual contents.

That is, since the channel 1 content is encoded with content N, andcontent N is encoded with content channel 1, receiving both encodedchannels of content allows decoder 242 to decode both channels ofinformation. At least one decoded content is made available from decoder242 of FIG. 2 to television receiver 26.

In the arrangement of FIG. 2, the unscrupulous subscriber who wishes toextract the encoded signal or the “key” is presented with the difficultythat he does not know how the encoding is performed. Secondly, he hasaccess for connection of his computer 34 only two possible connections(without disassembling the receiving arrangement 230). The firstpossible point to which he can connect his computer is at the outputterminal 230 o of receiving arrangement 230. At this location, he hasavailable either the encoded content, or the decoded content if he haspaid and the decoding information has been downloaded to the receivingarrangement 230. Presumably, the encoded content is not useful to himwithout more. If he has paid, then he has no incentive to attempt toextract the “key.” In the ideal situation, the “key,” which isinformation about which channels are related for encoding, can changefrom program to program, so the current decoding “key” is not useful forthe next following program.

The second possible connection which the subscriber can make is by wayof a further directional coupler or tap, illustrated as 33, to all theseparate physical channels flowing on the cable 20. These physicalchannels are manifested in the form of separate carriers. While thesubscriber may have a receiver, it is likely not a multichannel receiversuch as receiver arrangement 230 of FIG. 2. Consequently, even with asingle-channel receiver (RX) 35 connected to the tap 33 of FIG. 1, andwith one channel of encoded information available to the computer foranalysis, it will be very difficult to perform analysis to discover theencoding, because some of the relevant information is on anotherchannel, and is not available to computer 34 of FIG. 2.

One possible method for encoding the various content channels is byexclusive-or (XOR) processing. As an example of the encoding which ispossible using multiple information contents, consider four informationcontent streams At, Bt, Ct, and Dt. Information bit stream At isreplaced by a stream Ar=At XOR Ct; bit stream Bt is replaced by Br=AtXOR Bt; bit stream Ct is replaced by Cr=Bt XOR CT XOR DT, and bit streamDt is replaced by Dr=At XOR DT. As mentioned, the content which is usedfor the encoding can be changed from time to time, which may beimplemented in this example by changing the XOR method.

At the receiver arrangement 230 of FIG. 2, the digital packets areappropriately time-aligned to compensate for differences in time ofarrival, which can occur, for example, due to differences in group delayof the cable system and receiver filters at different frequencies. Whentime aligned, the original information content is retrieved orreconstituted by

-   -   original bit stream At=Ar XOR Br XOR Cr XOR Dr;    -   original bit stream Bt=Ar XOR CR XOR Dr;    -   original bit stream Ct=Br XOR Cr XOR Dr; and    -   original bit stream Dt=Ar XOR Br XOR Dr.        It should be noted that a characteristic of the XOR operation is        that the order in which the steps are performed does not affect        the result.

A similar algorithm can be employed across time in a single streameither before or after across transponder application (or both) to giveadded security.

Note that some channels can be sent in the clear and yet used to hide orencode the information in another bit stream. This is illustrated, inone form, in FIG. 3. In FIG. 3, encoder 12 a receives content 1 forencoding, and receives content 2 at its encoding signal input port 12ai, for processing content 1 to produce processed content 1′ forapplication to first upconverter 16 a. Information content 2 is appliedto upconverter 16 b without encoding, so is transmitted in the clear.

As another example of sending some information in the clear but usingthem to hide information, assume that At=Ar and Bt=Br are sent in theclear. Then, encoding can be performed by making transmitted bit streams

-   -   Cr=At XOR Ct XOR Bt; and    -   Dr=At XOR Ct XOR Dr.

The receiving arrangement 230 of FIG. 2 reconstitutes the desired bitstreams as

-   -   original bit stream At=Ar;    -   original bit stream Bt=Br;    -   original bit stream Ct=Ar XOR Br XOR Cr; and    -   original bit stream Dt=Br XOR Cr XOR Dr.

Note that the error correcting codes normally used across time could beused across transponders or physical channels for both error control andfor security.

FIG. 4 illustrates the logic flow in a digital satellite datatransmission system. As illustrated in FIG. 4, the information flowsfrom a transport formatter (not illustrated) by way of a path or node410 to a block 412, representing an encoder of the Reed-Solomon type.After encoding, the information flows by way of a path or node 414 to abyte interleaver illustrated as a block 416. The interleaved informationflows by way of a path or node 418 to a convolutional encoderillustrated as a block 420. The convolutionally encoded informationflows by way of a path or node 422 to a modulator of the QuadraturePhase Shift Keyed (QPSK) type. The modulated information is uplinked toa satellite, as suggested by block 426, and downlinked to a QPSKdemodulator 428. The demodulated information from demodulator 428 isapplied by way of a path or node 430 to a convolutional decoder 432. Thedecoded information from block 432 is applied by way of a path or node434 to a byte de-interleaver illustrated as a block 436. Thede-interleaved information from de-interleaver 436 is applied by way ofa path or node 438 to a further encoder block 440, which may be of theReed-Solomon type. The information leaves encoder 440 for a transportunformatter (not illustrated) by way of a path or node 442. Paths ornodes 410, 414, 418, and 422 represent mutually alternative locations atwhich multichannel or inter-channel dependency may be introduced to thesystem, and paths or nodes 430, 434, 438, and 442 represent mutuallyalternative locations at which inter-channel dependency may be removedand independent channel bits obtained.

FIG. 5 is a simplified block diagram of an overall communication systemaccording to an aspect of the invention, including a transmitter andreceiver portion. In FIG. 5, bits I₀ to be secured are applied by way ofa path 510 to a logic function block 520 and to a packet alignment block516. Additional bits I₁ and I₂ from other data streams are applied byway of paths 512 and 514, respectively, to packet alignment block 516and to transmitters (XMTR) 524 and 526. Packet alignment block 516aligns the packets I₁ and I₂ in time or makes them concurrent withpackets I₀, and applies the packets to function block 520 for encodingthe packets I₀ with information I₁ and I₂ to thereby produce I₀′information. The encoded I₀′ packets are applied to a transmitter block522. Transmitters 522, 524, and 526 produce signals to be transmitted.The I₀′, I₁ and I₂ signals are transmitted over channel 0, channel 1,and channel 2 paths 528, 530, and 532, respectively, to receivers (RCVR)534, 536, and 538, respectively. Receivers 536 and 538 recover the I₁and I₂ information, respectively. Receiver 534 recovers the encoded I₀′information. The recovered I₀′, I₁ and I₂ information are applied to apacket alignment function illustrated as a block 550, which aligns thereceived packets of information. The aligned I₀′, I₁ and I₂ packets ofinformation are applied to a decoding block 552, which extracts the I₀information.

The use of the invention makes it difficult for a “pirate” capturing asingle bit stream from a single physical channel together with readilyobtainable signals, such as the input-output (IO) signals from adecoding “smart card” to reverse engineer the security measures. Theinvention makes this technique difficult because bits from an unknown(to the pirate) set of physical channels, broadcast simultaneously or intemporal overlap, must be received and stored for analysis in order toperform the processing. Even if the pirate were somehow to obtain accessto all the physical channels, it is necessary to determine which of alarge number (possibly 4.3 billion) of dependency sets applies to agiven secured channel. If one has the dependency set, it is stillnecessary to identify the dependency relationship (the XOR arrangementin the embodiments).

The difficulty facing the pirate can be increased if the receiverarrangement (230 of FIG. 2) is in the form of an integrated circuit orgroup of related integrated circuits, as many of the signals which wouldbe useful for pirate analysis will not appear at any terminal of the ICor set of ICs, but are “consumed” internally.

The approach of the invention is based on a technological arrangementwhich is not now in common use, so presumably is not well known.Consequently, implementation of the method according to the inventioncould be accomplished without fanfare, or in a “stealth” fashion, toavoid alerting potential pirates.

Also, the use of multiple simultaneous physical channels could be usedto transmit by separate paths (a) the content and (b) the keyinformation for conventional encoding or encryption, so that access tomultiple physical channels is necessary in order to attempt to extractthe relevant information.

Those skilled in the art know that the processing of the multiplechannels of content to generate processed signals can be accomplished inmany possible manners, only one of which is the described XORprocessing. In general, interchannel dependency may be introduced withan N-input, 1-output logic function F, and removed with an N-input,1-output logic function G, where F and G are such that I0=G(F(I0, I1,I2, . . . , In), I1, I2, . . . , In) is an identity. F=G for F=(I0 XORH(I1, I2, . . . , In), where H is any n-variable logic function. An XORcascade is such a function. In the context of this invention, separatephysical channels may be implemented by frequency separation in thecontext of electromagnetic transmissions (television or radio, forexample), or by separate packet timing in time-division multiplexsystems, or by separate orthogonal codes in the context of code-divisionmultiplexing.

A method according to an aspect of the invention is for securelytransmitting first information (I₀) from a first location (508) to asecond location (525) by way of a first channel (520, 522, 528, 534).The method comprises the steps of, at the first (508) and second (525)location, acquiring second (I₁) and additional (I₂) information which isindependent of the first information, and time aligning (516, 550) thesecond (I₁) and additional (I₂) information at both the first (508) andsecond (525) locations. At the first location (508), the firstinformation (I₀) is related with the second (I₁) and additional (I₂)information by means of a first function (F (I₀, I₁, I₂)) to therebygenerate a transmitter signal (I₀′) for transmission, and the resultingsignal (I₀′) is transmitted from the first location (508) to the secondlocation (525) by way of a first signal channel (528). At the secondlocation (525), the transmitter signal (I₀′) is related to the second(I₁) and additional (I₂) information with a second function (G(I₀, I₁,I₂)) which is the reverse of the first function (F (I₀, I₁, I₂)) tothereby recover the first information (I₀). In one particular mode ofthe method, the first and second functions are XOR functions. The stepof acquiring the second (I₁) and additional (I₂) information at thesecond location (525) may includes the steps of receiving the second(I₁) and additional (I₂) information by way of individual, independentsignal channels (512, 524, 530, 536; 514, 526, 532, 538). In aparticularly advantageous version of this method, at least some of thesecond (I₁) and additional (I₂) information is transmitted from thefirst location (508) to the second location (525). The step oftransmitting at least some of the second (I₁) and additional (I₂)information from the first location (508) to the second location (525)may be performed by way of at least one signal channel (512, 524, 530,536; 514, 526, 532, 538) independent of the first signal channel (520,522, 528, 534). The step of transmitting at least some of the second(I₁) and additional (I₂) information from the first location (508) tothe second location (525) may be performed by transmitting each of thesecond (I₁) and additional (I₂) information by way of a single signalchannel independent of the first signal channel for each individual oneof the second and additional information (512, 524, 530, and 536 for I₁;514, 526, 532, and 538 for I₂). In a particularly advantageous versionof the method, the step of at the second location (525), relating thetransmitter signal (I₀′) to the second (I₁) and additional (I₂)information with a second function (G(I₀, I₁, I₂)), is performed inconcert with a receiver (230) able to simultaneously receive multiplechannels including the first signal channel, and the signal channels foreach individual one of the second and additional information.

A method according to an aspect of the invention is for securelytransmitting first and second information from a first location (8) to asecond location (224). The method comprises the step of processing thefirst information (1) by means of at least the second information (N) tothereby generate processed first information (1′). The secondinformation (N) is processed by means of at least the first information(1) to thereby generate processed second information (N′). The processedfirst (1′) and second (N′) information are transmitted separately by wayof independent first (f1) and second (fN) physical channels,respectively, to the second location (224). At the second location (224)the processed first information (1′) is reverse processed by use of atleast the processed second information (N′). Reverse processing of theprocessed second information (N′) may be done by the use of at least theprocessed first information (1′).

In a particular mode of the method, the step at the second location(224) of reverse processing the processed first information (1′) by useof at least the processed second information (N′) includes the step ofindependently receiving the processed first information (1′) from thefirst independent channel (f1) and independently receiving the processedsecond information (N′) from the second independent channel (fN). In apreferred mode of this method, this latter step is performed by anintegrated circuit.

According to another aspect of the invention, a receiver (230) isprovided for simultaneously recovering at least first information (1)received in processed form (1′) by way of a first independent physicalchannel (f1) and second information (N) by way of a second independentphysical channel (f2). The first information (1) transmitted over thefirst physical channel (f1) is processed before transmission inconjunction with second information (2) to generate processed or encodedinformation (1′). The second information (N′) is transmitted to thereceiver (230) over a second independent channel (fN). The receivercomprises means (240 a) for receiving the processed first information(1′) from the first physical channel (f1), and also comprises means(240N) for receiving the second information (N) from the secondindependent channel (fN). A processing means (242) processes the firstprocessed information (1′) in conjunction with the second information(N) to extract the first information (1) from the first processedinformation (1′). In that case in which the information transmitted overthe second channel (fN) is encoded to form second processed information(N′), the processing means (242) also extracts the original secondinformation (content N), and for this purpose the receiver (230)comprises further processing means for processing the first processedinformation (1′) with the second information (N′) to extract informationrelating to the form of the second information (N) before the processingwith the first information (1).

In a preferred embodiment of this receiver, all or most of the describedfunctions are contained or lie within a single integrated circuit.

1. A receiver apparatus, comprising: a plurality of receivers capable ofsimultaneously receiving a plurality of program signals from respectiveindependent channels associated with each of the receivers; and decoder,coupled to the plurality of receivers, for processing a first encodedprogram signal received from a first transmission channel using a firstfunction and a second program signal received from a second transmissionchannel, which is independent of the first transmission channel, tothereby decode the first program signal.
 2. The receiver apparatus ofclaim 1, wherein the decoder includes means for time aligning the firstencoded program signal with the second program signal prior to decodingthe first encoded program signal.
 3. The receiver apparatus of claim 1,wherein the decoder decodes the first encoded program signal using thesecond program signal and the first function during a first period oftime, and decodes the first encoded program signal using the secondprogram signal and a second function during a second period of time. 4.The receiver apparatus of claim 1, wherein the decoder decodes the firstencoded program signal using the second program signal received from asecond transmission channel and the first function during a first periodof time, and decodes the first encoded program signal using a thirdprogram signal received from a third transmission channel, which isindependent of the first transmission channel, during a second period oftime.
 5. The receiver apparatus of claim 4 wherein the decoder changesthe decoding between the second program signal and the third programsignal on a periodic basis.
 6. The receiver apparatus of claim 1,wherein the second program signal is encoded, and the decoder decodesthe second program signal using the decoded first program signal and asecond function.
 7. A receiver apparatus, comprising: means forsimultaneously receiving a plurality of program signal transmitted viarespective independent transmission channels; decoder means, coupled tothe receiving means, for processing a first encoded program signalreceived from a first transmission channel using a first function and asecond program signal received from a second transmission channel, whichis independent of the first transmission channel, to thereby decode thefirst program signal.
 8. The receiver apparatus of claim 7, wherein thedecoder means includes means for time aligning the first encoded programsignal with the second program signal prior to decoding the firstencoded program signal.
 9. The receiver apparatus of claim 7, whereinthe decoder means decodes the first encoded program signal using thesecond program signal and the first function during a first period oftime, and decodes the first encoded program signal using the secondprogram signal and a second function during a second period of time. 10.The receiver apparatus of claim 7, wherein the decoder, means decodesthe first encoded program signal using the second program signalreceived from a second transmission channel and the first functionduring a first period of time, and decodes the first encoded programsignal using a third program signal received from a third transmissionchannel, which is independent of the first transmission channel, duringa second period of time.
 11. A method for processing an encoded programsignal, comprising the steps of: simultaneously receiving the encodedprogram signal over a first transmission channel and a second programsignal over a second transmission channel, which is independent of thefirst transmission channel; and decoding the encoded program signalusing the second program signal and a first function.
 12. The methodaccording to claim 11, further comprising the step of time-aligning theencoded program signal and the second program signal prior to decodingthe encoded program signal.
 13. The method according to claim 11,wherein the decoding step comprises decoding the encoded program usingthe second program signal and the first function during a first timeperiod, and decoding the encoded program using the second program signaland a second function during a second time period.
 14. The methodaccording to claim 11, wherein the receiving step comprisessimultaneously receiving a third program signal on a third transmissionchannel that is independent of the first transmission channel, thedecoding step comprises decoding the encoded program signal using thesecond program signal and the first function during a first time period,and decoding the encoded program signal using the third program signaland the first function during a second time period.
 15. The methodaccording to claim 11, wherein the second program signal is encoded, andthe decoding step comprises decoding the second program signal using theencoded program signal and the first function.